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超声弹性成像有希望成为生物软组织病变诊断的有效手段,本文论述了软组织散射元准周期规则分布导致超声散射信号相干峰产生的机理,提出利用AR幅度倒谱估计散射元平均间距及其变化,结合组织外加应力来估计软组织内局部杨氏弹性模量,结果表明,该方法能有效地测量软组织内局部杨氏弹性模量,轴向和侧向空间分辨力分别为2.5mm和1.5mm,可用于在体软组织弹性成像,最后讨论了软组织弹性测量中的具体问题。 相似文献
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生物软组织力学活体测试技术进展 总被引:1,自引:0,他引:1
本文综述了近年来有关生物软组织如皮肤、粘膜、肌腱、肌肉、神经和血管等活体状态下进行力学测试的新技术和新的试验装置,讨论了离体和活体生物力学性质之间存在差别的可能因素,以及活体生物软组织力学试验方法在临床应用中的意义。 相似文献
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根据钢丝软轴基本参数的变化,确定其受载后其它几何尺寸的变化量,由此导出软轴两端相对扭转角进而得到钢丝软轴抗扭刚度的计算公式,此外,笔还在扭转试验机上对钢丝软轴的抗扭刚度进行实验测量,结果证实本理论计算值吻合于实际测量值。 相似文献
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生物软组织力学在研究生理、病理上具有很重要的地位。例如,动脉壁由于血压的作用而产生的应力和变形的问题,在了解心血管系统的生理和病理方面已得到了医学界的承认和重视。下面要谈生物软组织力学的另一方面的作用。 相似文献
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目前中小桥梁日常安全巡检存在对检查人员依赖性高、缺乏可量化的科学依据等不足。针对这些问题,本文提出了一种利用高斯曲率极值点对结构进行损伤识别的方法。将桥面视为受弯弹性薄板,根据弹性薄板的弯曲理论得到了在荷载作用下结构刚度变化与桥面弯曲程度(高斯曲率)的理论关系,并由此推导了高斯曲率对结构刚度损伤的敏感程度公式。通过有限元建立了一座简支T梁模型,并在主梁肋板上设置不同高度、不同位置和不同数量的裂缝来模拟结构刚度损伤。计算了在自重作用下,裂缝高度、位置、数量与桥面高斯曲率变化的关系。分析结果表明,桥面的高斯曲率分布清晰地映射了结构的刚度分布,高斯曲率极值点明确地指征了桥梁的损伤位置。借力三维激光扫描等全息现代测量技术,本文的研究成果为高效量化的桥梁结构损伤识别提供了有效的分析手段。 相似文献
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刚接或半刚性连接的组合梁在荷载作用下,在梁的长度范围内既有正弯矩作用段,又有负弯矩作用段,由于组合梁截面在正弯矩作用和负弯矩作用下截面抗弯刚度不一致,因而在弯矩为零的点处梁的截面抗弯刚度发生突变,而组合梁框架分析的关键是确定组合梁刚度突变分界点的位置及确定在整体分析中所采用的等效梁的刚度。本文根据应变能相等的原理对钢结构框架中组合梁的等效抗弯刚度进行了研究,推导了其等效刚度的表达式,并给出不同荷载作用形式下刚接框架组合梁等效刚度简化计算公式,为组合梁钢框架的整体分析提供了便利。最后分析了水平荷载以及梁柱连接特性对组合梁等效刚度的影响,分析结果表明,采用本文提出的组合梁等效刚度进行半刚性连接框架整体分析偏于安全。 相似文献
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本文提出了用于岩土弹塑性有限元分析的隐式积分弹性刚度算法。该算法既具有隐式积分法精度好、效率高、无条件稳定等优点,也具有弹性刚度法中刚度矩阵正定、对称的特点,更重要的是它避免了传统切线刚度法在处理岩土非相关联塑性流动和屈服面“角点”所遇到的非对称性和奇异性计算问题。通过算例分析了该算法的精度、效率 相似文献
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Luis A. Godoy 《Meccanica》2006,41(5):529-538
This paper studies the historical and epistemological approaches followed by historians of the theory of elasticity. The authors chosen are Todhunter and Pearson, Love, Timoshenko, and Truesdell, who are perhaps the most important historians in English language since the second half of the nineteenth century. It is shown that the historical purpose has changed from one historian to the next, ranging from history as a compilation of what is known to criticism of the evolution of elasticity. The path of progress is investigated and again there are significant differences between historians although overall they have a sense of confluence towards some form of truth. The relation between history and theory is identified as a recurrent theme. And the epistemology in each author, although not explicitly stated, is seen to change following the main trends in their times or before. Some possible avenues of research are mentioned towards the end. 相似文献
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G. A. Vanin 《International Applied Mechanics》2007,43(1):54-63
A multimoment theory of elasticity of inhomogeneous media is used to develop algorithms for determining a sequence of essentially
independent fundamental parameters associated with the structure, composition, and characteristics of the medium components.
The general form of stress concentration factors is established by analyzing specific models of media. It is found that the
mean tangential stresses in a fibrous medium with a transverse stress state are asymmetric. As an example, the methods are
used to solve specific problems for plates and shells
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Translated from Prikladnaya Mekhanika, Vol. 43, No. 1, pp. 66–76, January 2007. 相似文献
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Semi-Lagrangian methods are now perhaps the most widely researched algorithms in connection with atmospheric flow simulation codes. In order to investigate their applicability to hydraulic problems, cubic Hermite polynomials are used as the interpolant technique. The main advantage of such an approach is the use of information from only two points. The derivatives are calculated and limited so as to produce a shape-preserving solution. The lack of conservation of semi-Lagrangian methods, however, is widely regarded as a serious disadvantage for hydraulic studies, where non-linear problems in which shocks may develop are often encountered. In this work we describe how to make the scheme conservative using an FCT approach. The method proposed does not guarantee an unconditional shock-capturing ability but is able to correctly reproduce the discontinuous flows common in open channel simulation without any shock-fitting algorithm. It is a cheap way to improve existing 1D semi-Lagrangian codes and allows stable calculations beyond the usual CFL limits. A basic semi-Lagrangian method is presented that provides excellent results for a linear problem: the new techniques allow us to tackle non-linear cases without unduly degrading the accuracy for the simpler problems. Two one-dimensional hydraulic problems are used as test cases, water hammer and dam break. In the latter case, because of the non-linearity, special care is needed with the low-order solution and we show the advantages of using Leveque's large-time step version of Roe's scheme for this purpose. 相似文献
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Hiroshi Yabuno 《Nonlinear dynamics》1996,10(3):271-285
For a beam subjected to electromagnetic force, magnetoelastic buckling due to the increase of such force is theoretically investigated by taking account of the nonlinearity of the electromagnetic force and the elastic force of the beam. Using Liapunov-Schmidt method and center manifold theory, the equilibrium space, the bifurcation set and the bifurcation diagram are theoretically derived. Also, the effect of the higher modes other than the buckling mode on the mode shape of the postbuckling state is discussed. Furthermore, a control method to stabilize the magnetoelastic buckling is proposed, and the unstable equilibrium state of the beam in the postbuckling state, i.e., the straight position of the beam, is stabilized by controlling the perturbation of the bifurcation. 相似文献
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A technique is developed for determining the thermoviscoelastoplastic geometrically nonlinear axisymmetric stress–strain state of laminar shells of revolution under loads that induce meridional stress and torsion. The technique is based on the hypotheses of rectilinear element for the whole stack of layers. The relations of the theory of deformations along paths of small curvature are used as equations of state. The solution is reduced to the numerical integration of a system of ordinary differential equations. The technique is tried out by a test example and illustrated by determining the geometrically nonlinear thermoviscoelastoplastic state of a corrugated shell 相似文献
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In this paper, the wake effect on drag factor in the axisymmetric Oseen flow of the finite clusters of equally spaced spheres
with same size is studied. Putting the Oseen lets on the centres of all the spheres, the series solution of the problem is
obtained. By truncating the infinite series and applying the collocation method to solve a set of the linear algebraic equations,
the approximate solution of the Oseen flow of finite clusters of spheres and the drag factor for each sphere are presented.
The effect of the sphere number and spacing on the drag factor of each sphere under different Reynolds numbers are calculated
and the wake effect as well as the shielding effect and the end effect are revealed. The influence of various parameters on
the effects is considered and compared with the corresponding results of the Stokes flow. The convergence of the method is
also studied numerically in this paper. 相似文献
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This work investigates the trajectory method [1] for thereconstruction of ordinary differential equations (ODEs) from timeseries. The potentials of the method are analyzed for dynamical systemsdescribed by second- and third-order ODEs, focusing in particular on therole of the parameters of the method and on the influence of the qualityof the time series in terms of noise, length and sampling frequency.Typical models are investigated, such as the van der Pol, the linearmechanical, the Duffing and the Rössler equations, resulting in arobust and versatile method which is capable of allowing interestingapplications to experimental cases. The method is then applied to themeasured time series of a nonlinear mechanical oscillator, a typicalvelocity oscillation of the bursting phenomenon in near-wall turbulenceand the averaged annual evolution of rainfall, temperature andstreamflow over a hydrological basin. 相似文献
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Hai-Chang Hu 《Acta Mechanica Solida Sinica》1992,5(2):175-182
It is proved in this paper that the functionals of equivalent variational principles are different essentially only in terms of weighted residues. Consequently, the simplest method for constructing equivalent variational principles is to add weighted residues to known functionals as first used by Courant [4]. 相似文献